HESCOMP is a helicopter sizing and performance computer program very similar in format and operation to VASCOMP II, the V/STOL Aircraft Sizing and Performance Computer Program. This similarity is dictated by the requirement to obtain compatibility in both usage and results when using HESCOMP and VASCOMP II in helicopter-V/STOL aircraft comparative design studies. The program's purpose is to rapidly provide helicopter sizing and mission performance data. The program can be used to define design requirements, such as weight breakdown, required propulsive power, and physical dimensions of aircraft which are designed to meet specified mission requirements. It is also useful in sensitivity studies involving both design trade-offs and performance trade-offs.